1. Technical Field
This disclosure relates to heat exchanging systems for motor vehicles.
2. Background Art
Vehicle manufacturers are under pressure to improve the fuel consumption and emissions figures produced by standard drive cycle tests of their vehicles. Drive cycle tests, such as the European drive cycle (NEDC) start with the engine and transmission cold. Most journeys start with a cold engine and fuel consumption and exhaust emissions are worse for a cold powertrain than when it is at normal operating temperatures. From a cold start, the engine metal, coolant, engine oil, transmission oil, and exhaust treatment systems take a significant amount of time to warm up. These components are consequently not operating at their optimum temperatures for a significant portion of the drive cycle and this has a detrimental effect on fuel economy and emissions.
During cold start or early warm-up operation, the engine will not require any cooling. To reach maximum fuel efficiency in the shortest possible time, it is advantageous to provide for heating lubricants, such as the engine oil and transmission oil, up to some optimum temperature.
GB-A-2429763 discloses a vehicle system in which heat from exhaust gases is used to warm coolant which, in turn, is used to warm the engine oil.
It is also known for a vehicle to have an exhaust gas recirculation (EGR) system. See, for example, US2006/0005791. Therein is described a cooling system whereby an engine coolant circulates through an exhaust gas heat exchanger for the purposes of cooling exhaust gases prior to diverting the gases to the inlet manifold of the engine.
Engine oil warms up slowly in internal combustion engines, leading to higher friction due to higher viscosity of the oil, especially from ambient temperatures starts. In known systems oil temperature is initially linked to coolant temperature and coolant is more effective at cooling when cold than when the engine is hot. A water-cooled EGR system will also stay cold during the early stages of a drive cycle unless a bypass is fitted. Cold EGR gas tends to cause higher levels of carbon monoxide and hydrocarbons than is desirable.